1. Field of the Invention
This invention relates to an automatic print head position adjusting mechanism, and more particularly to an automatic adjusting apparatus for printers such as a dot printer and the like which automatically adjust a space or a gap between a printing head and a printing paper according to the thickness of the printing paper to set the printing head to the optimum position.
2. Prior Art
Sharp and clear characters or legends can not be printed unless the space between the printing head and the paper is properly adjusted when the characters are printed. Furthermore, this space should be suitably adjusted so as to accommodate the thickness of the printing paper.
The apparatus which have been used to this end are disclosed as in Japanese Patent Laid-Open Applications Nos. Sho 60-56202 and 61-199969.
Application No. Sho 60-56202 deals with an automatic paper thickness detector mechanism for a printer, which comprises a carriage having one end loosely supported by a fixed spindle and having the other end slidably and loosely mounted in an eccentric member. The carriage is movable in the axial direction of the rotary shaft parallel to the fixed spindle. The paper thickness detecting mechanism further includes a paper thickness detecting member adapted to abut against a platen when the carriage is swung, a spring for energizing the rotary shaft toward a part of the platen, and a drive motor for rotating the rotary shaft a certain extent in a direction opposite to the direction in which the spring is energized.
Application No. Sho 61-199969 discloses an automatic head gap adjusting mechanism for a printer which includes a movable printing head energized to an advanced position, a platen movable back and forth in opposition to the print head, and a sensor for detecting when the print head is a given distance away from the platen. The head gap adjusting mechanism operates such that the platen is advanced to the print head with the printing paper being between the print head and the platen, and that the platen is moved away a given distance from the starting point; i.e., to a where the sensor serves for detection.
In addition to the aforementioned apparatus and mechanisms, prior art print head adjusting mechanisms have employed step-out methods for a stepping motor, slip methods relying on a torque limiter and pre-sensing methods.
Application No. Sho 60-56202 discloses a system in which it is difficult to obtain accuracy when printing and thus fails to maintain print quality since a carriage is pivoted about the fixed spindle. A disadvantage derived from Application No. Sho 61-199969 is that the printer is required to provide a greater space between the print head and platen since the positioning of the platen is based on moving the print head back away from the platen and by an accompanying advancement and moving away of the platen, thereby adjusting the head gap.
A disadvantage of apparatus or mechanisms which use a step-out method for the stepping motor is the difficulty in recognizing a layer just before the print head is moved from the step-out position and back therefrom; i.e., the step-out position. This involves a loss to the operation under which less than four steps will destroy positional accuracy of the print head and deteriorate printing quality.
A drawback to pre-sensing methods providing a given feed system is that paper thickness sensors are costly and require a more constructive space.